In the optical industry, prescription eyeglass lenses are typically conformed to a predetermined inside curve by sweeping a diamond grinding wheel across a lens blank. The diamond wheel generally has a hollow semi-spherical configuration and is rotated by a quill about an axis extending through the center of the semi-spherical diamond wheel. The quill is, in turn, rotatably supported on a number of adjustable slides that are adjusted to vary the sweep of the diamond wheel and to thus control the thickness and curvature of the generated lens.
In recent years, there has been increased consumer demand for lenses made not only from glass and CR-39 plastic material, but also from polycarbonate material. Polycarbonate material, for example, is often viewed as superior to glass and CR-39 plastic materials because it offers improved strength and durability with substantially reduced weight. Unfortunately, polycarbonate material requires a different type of diamond grinding wheels than does glass material, and the diamond wheels for polycarbonate material are generally shorter (axially) than diamond wheels for glass material. Consequently, unless more than one lens generating machine is used, it is necessary to change grinding wheels each time the operator changes between glass and polycarbonate lens blanks.
Due to tolerances, all grinding wheels are of slightly different (axial) length, even when the wheels are new. Furthermore, grinding wheels for glass material undergo substantially more wear than do grinding wheels for polycarbonate material. After experiencing some selected degree of wear, grinding wheels for glass material are frequently retrued, a procedure that further shortens (axially) the wheel. Thus, variations between the axial lengths of grinding wheels for glass and polycarbonate materials are typically increased over time as the wheels wear.
Thus, when a lens grinding machine is used to generate lenses of both glass and polycarbonate on a frequent interchangeable basis, it becomes necessary to frequently readjust the machine to compensate for the differing lengths of the different wheel types.
It generally requires an average time of one hour to change diamond wheels and recalibrate the distance between the diamond wheel and the lens blank. Hence, when the capability to alternate between glass and polycarbonate lenses on a rapid basis is required, it is necessary for a lens grinding laboratory to have two separate lens generating machines. This, of course, necessitates a substantial increase in capital expenditure over a single lens generating machine and requires additional floor space in the lens grinding laboratory.
It is also occasionally necessary to adjust the position of a diamond wheel for glass material in a lens generator to compensate for wear and retruing. In many systems, wheel wear and retruing compensation is accomplished in the same general manner as the previously described distance compensation for new polycarbonate wheels that are different length than diamond wheels for glass material. Specifically, the quick change diamond wheel is removed from the lens generating machine and placed on a gauge table. Once the diamond wheel wear is gauged, the quick change quill is disassembled and shims of appropriate size are placed on the quill to axially reposition the cutting face of the worn diamond wheel to the same relative machine position as original wheel cutting face.
In recognition of the above-mentioned disadvantages, one major manufacturer of lens generating machines has developed a system for changing diamond wheels in lens generating machines in slightly less than five minutes. In the system, known as the Quick Change Diamond System from Coburn Optical Industries, Inc. of Muskogee, Okla. the original quill for the lens generating machine is replaced with a quick change quill that, in essence, uses replaceable shims to axially increase or decrease the quill length. This permits an operator to quickly change a diamond wheel for polycarbonate material and a different diamond wheel for glass material. Furthermore, with such a quick change quill, the interface surfaces of the wheel for polycarbonate material is located at the same relative position on the machine as the corresponding surfaces for a diamond wheel for glass material.
Although the above described Coburn Quick Change Diamond System offers substantial advantages over earlier methods of changing diamond wheels, the time demands for changing diamond wheels and compensating for wear remains excessive, even under this improved system. These time demands are Particularly troublesome when the lens generating machines are being used in what the trade now refers to as "optical superstores" wherein the lens grinding laboratory is located in a high volume retail optical store and eyeglasses are provided to customers in a very short time, as, for example one hour or less.